RWS 34 vs Xisico XS-B28: A Magnum Tuning Project

This page preserves a discussion thread from the original AirgunOne.com community forum, active from 2008 until the site went offline. It's republished here for reference, in full, including the community banter. If you're a contributor to this thread and would like something removed or credited differently, contact info@airgunguide.com.

The Project

super6 wrote: "Here's some pics to get your attention. I'm using some literary license and using the RWS 350 photo since the B28 is in pieces. The B28 stock is lighter in color but otherwise the two are identical. So what's a 34 have to do with a B28? Stay tuned........"

Robin A wrote: "Keep the info.coming,I have both rifles and just got a RWS 36 for peanuts.......................Robin"

C.A.P wrote: "Ray you have DROOP !"

super6 wrote: "Chris: when you turn 58 then talk to me about droop!!!! Things kick off Saturday with background info, pix, and tuning, and what may turn out to be a very interesting project for the 34. Patience my friends as things are nuts on the homefront and sometimes all the VA meds don't work very well. Chris will have some awesome things to discuss shortly also for his B28 and my 350 as the test subjects. Let's just say, we're pushing the envelope(s)."

njphil wrote (quoting Robin A's post above): "Lucky dog, Im looking for a 36"

The Two Guns, Measured

super6 wrote: "The reason for the 34 is that Chris and I are working on an upgrade for the B28 and the RWS 350. I took down my 34 because we needed some spring and piston measurements among others. The guinea pigs for that project are my 350 and Chris's B28."

"My B28 will receive a tune with all stock parts except for a new piston seal and some spacers. The 34 will get a tune along with a new piston seal and Pyramyd's Air Venturi RWS spring and delrin guides kit for the 34 and other Diana models. I had bought it some time ago for my Ruger but it didn't fit so I used Jim's spring and Apex seal in the Ruger. The Ruger is a copy of the 350, with smaller dimensions, not the 34. So anything I do with the B28 applies to the Ruger also."

"When both guns are done I'll chrono both and compare performance pre- and post tune. After that, I'll attempt to take the 34 to an even higher level of performance with a new aftermarket spring that, on paper, could be a big bump in power. I hope my measurements were good."

super6 wrote: "Referring to the second picture: the 34 has a 12.8" receiver, a 5.19" piston, and a spring with a set length of 11.25", 0.128" wire, and 33 coils, the 28 has a 15.19" receiver, a 6.31" piston, and a spring with a set length of 14.25", 0.126" wire, and 40 coils."

"The trigger assemblies are identicle except the 28 has a metal trigger. The rear spring guides are similar with a thin machined washer for the springs to ride on. The 28 (and Ruger) has a sheet metal 'can' that the spring goes into with two spacers, which all goes into the piston. It's purpose is to prevent the cocking foot/shoe from hanging up on the spring while cocking and then closing the breech. It may also help stabilize the very long spring. Also, notice the articulated cocking arm on the 28 which reduces the effort needed to cock the gun by increasing leverage...it works well."

"In short the 28/350 is a 'stroked' 34 with only two major design differences. The RWS piston seals are blue and clearly better than the 28 seal. In fact, if the RWS seal is cheaper from Umarex, I recommend buying from them as opposed to a more expensive aftermarket seal...for all RWS/Diana models. As far as things like blueing, metal work, wood, etc., the RWS is better, but not by much. The 34 was COMPLETELY dry in the powerplant and the seal is damaged from assembly. The B28 was almost as bad with only a tiny amount of Chicom turd brown lube IN the piston and a nicked up seal. The moral of the story is that any gun these days should get at least a lube tune and probably a new piston seal up front. Putting a bunch of pellets through the gun until it 'breaks-in' doesn't make a lot of sense to me. Maybe a string or two to get some baseline numbers using a chrono but no more. Some of the British guns, the Mendozas, Turkish guns and some others sometimes come with too much lube which is equally or even harder on a new gun."

"This is TOTAL HERESY but it works, for two years and counting......a lube in a can. Buy a spray can of white lithium grease and spray the piston and spring through the cocking slot really well. Don't spray the compression area ahead of the piston. Fire the gun a bunch of times, remove the stock, and spray out the excess with compressed air and clean up the mess. Oh, and do the same to the trigger assembly. This was done to a 34 about 2 years ago and it will still outshoot 95% of the untuned 34's out there. It works. Have I done it to any of my guns? No. But I may do it to a $69 Daisy Powerline 1000 refurb I've got...just for grins."

"Out of the box, the 34 (.177) averaged 794fps using JSB 8.44gr pellets. The 28 (.22) averaged 824fps using Crosman Pointed 14.3 gr pellets."

"Now, I'm off to do some de-burring, honing, and polishing and will post more later today along with my way of lubing a springer and more pictures. Also, my 34, 350, and the B28 all have breech seals that are essentially flush with the breech block, so I'll be doing some shimming. Later.... Ray"

brianag618 wrote: "Where did you find the stock if you do not mind me asking, I may want to replace the one on my RWS 34 Panther. Also do you have any idea where I can get a good stock (cheap) for the RWS 54, looking to dress this one up a bit and replace the old one. (we are in the same age bracket I am 57, us old timers need to stick together) Brian Goodloff Security Consultant"

super6 wrote: "Brian, the 34 stock is the RWS/Diana 34 Meisterschutze Pro stock. Contact Umarex for a price, which won't be cheap. But your gun will drop right in."

"All the grinding, hacking, and hammering is done and I'm taking a break. I need to clean everything and begin lubing and reassembly. I had expected a spring and some seals today but looks like Monday. I have a couple of Tesla seals that should work. I'll post some pix and a description of the Air Venturi spring and guide upgrade for the 34 along with the reassembly of both guns."

"NEWS FLASH!!!! Have had a number of conversations with Chris (C.A.P.) and the Mongo B28/RWS350 project is making major progress today. I'll get him to post something soon. Also, see the next post and check out what Rich in Mich returned to me today............."

super6 wrote: "Check out Rich in Mich's handiwork....haven't had a chance to play with it yet."

C.A.P wrote: "OK, I have been at it all day> Machining pistons and taking this thing down over 6 times already. Its showing by first impressions to be a mover and a shaker. It has been shot already about 150 times. The seal is starting to break in. I will get some hard numbers with results soon. Here is what I have been looking at for the last few days and today has been a real test in patience. I had to do some real custome stuff to get this thing together. You can see my Power spring there !"

Building the Tune

super6 wrote: "Here's the Air Venturi pro Guide Spring Retainer sold by Pyramyd for $89. It's under accessories/parts. I had bought it for my Ruger around November last year. It wouldn't fit the Ruger due to its can in piston design like the 350 and the B28. I then bought the spring and piston seal from Jim Maccari's RWS 34 kit which worked fine in the Ruger which was the first springer tune I did."

"I kept the Air Venturi kit as I figured I'd get a 34 eventually. It is for the RWS/Diana 34, 36, 38, 48, 52, and 54 with either the T01 or T05 triggers. It's one size fits all. It consists of two delrin guides and a spring and a touch of clear lube. The spring is 9.69" long with 0.136 wire and 29 coils. Above it is the stock spring (dimensions earlier in the thread) and rear spring guide. What we have is a female rear delrin spring guide versus the male 'plastic' factory guide. The front spacer is a male delrin guide with a base and 3 spacers versus the stock 34 spring end riding on the rear of the piston face."

"It is designed as a drop in tune. You can open any of the models listed, remove the trigger assembly, the rear spring guide and the spring and then simply drop this in and reassemble the gun....that's it. No twang, a smoother firing cycle, and a possible gain in fps. There is a small amount of clear lube on the spring in the rear guide and a smaller amount on the spring and front guide. No tar and no moly."

"I'm stacking the deck by de-burring, sanding, honing, and lubing the powerplant and adding a new piston seal. I'm expecting a much smoother firing cycle, smoother cocking, and a bump in power. We'll know tomorrow."

"The B28 is getting a full tune with a new piston seal and one or two stainless spacers acting together as a poor man's top hat. The normal full tune for a RWS 350 (and now the B28) is a spring, rear guide, piston seal, and a top hat plus lubes. So my B28 will be a tweaked but basically stock gun."

"When Chris and I get the BIG 350 and 28 project done to our satisfaction, we'll be releasing more info and hard numbers, in a matter of days. And my 350 will get the exact same makeover both to compare and prove it's viable in both guns."

"Since we had my 34 apart, we are addressing the RWS 34 in parallel. Come Monday or Tuesday, I will, if successful, release hard numbers above and beyond the 'stage 1' upgrade discussed above. Tomorrow you'll have the tuned B28 chrono numbers and the stage 1 RWS 34 numbers, unless I can finish them tonight. Right now I'm blueing bare metal on the receivers to protect from rust and getting ready to tweak the triggers."

"The trigger assemblies are the same but the German trigger parts are of a better quality than the Chicom parts in the B28. I expect both to have an approximate trigger pull of about 1.5lbs/two-stage. If you can't get your B28 to perform as well as you like, you can buy individual German trigger parts from Umarex. I'm replacing a single spring in each and about 10 seconds of polishing. That's all it takes. PM Chris for the link for the aftermarket trigger springs and pm me your email addy if you want a copy of the RWS T05 trigger tune."

"Back to work....more to come with pix."

super6 wrote: "The following is an overview of how I tune my guns. I'm assuming you have at least read an article or two on tuning. I don't believe there is one perfect way to do a tune so 'take what you like and leave the rest.'"

"First I de-burr all the sharp edges, inside and out, on the receiver tube and the piston. I'll start with a Dremel and a small stone, then use small jeweler's or hobbyist's files, and finish up with 400 grit sandpaper by hand."

"Then I hone the cylinder and the inside of the piston with 400 grit paper in a flapper made with 3/8" dowel with a slot in one end. Since the Diana models have the center shaft which engages the trigger sear, I use a section of cleaning rod with a .22 plastic patch holder with a small piece of sandpaper. I do have a brake cylinder hone with 400 grit stones with an extension for honing the compression area ahead of the cocking slot that I'll use if the cylinder looks really rough. Then I go back and do it all again with 600 grit paper."

"After removing the piston seal, I sand the piston with 400 and then 600 grit paper wherever metal contacts metal. I lightly round sharp edges on the piston and on the face of the piston where the seal goes on. I'm trying to prevent a sharp edge scuffing the cylinder wall. Clean everything using brake cleaner, 3M adhesive remover, mineral spirits, googone, or hot water and dish detergent (dry fast and start lubing to avoid rust)."

"Lubing is the most controversial. I use a dowel with the end wrapped with paper towel held on with a rubber band. I use SuperLube spread over the paper towel and apply a THIN coat from one end to the other. Use a flashlight and check the inside. If you missed a spot, lube it. If too much, use a clean paper towel piece on the end of the dowel and remove the excess. Set aside."

"Take the piston and put a THIN coat of SuperLube on the piston face and cone. Do the same to your piston seal on the bottom and the center hole. Lay your seal face down, insert the piston cone in the hole and press down....should pop on easily."

"Coat entire piston, inside and out with a VERY THIN coat of moly, from behind the seal and back. Basically wherever metal contacts metal and to prevent rust. Set aside."

"Polish spring ends LIGHTLY. Put a THIN coat of moly on the end and the coils that sit in the piston. If the other end is riding on a washer, put a little moly there. I put a THIN coat of clear lube or any synthetic lube on the synthetic rear spring guide and the coils that rest on the spring guide. Dab a small amount of black tar on the outside of the central coils between the piston and the rear guide. Set aside."

"Insert piston into cylinder taking care not to nick or cut the seal and push it down to the end. Put a piece of clean paper towel on your dowel and mop up 95% of the SuperLube from the piston back. Then apply a very THIN coat of moly in the cylinder from the piston back. Drop in the spring and guide and reassemble the powerplant. Done."

"REMEMBER...LESS IS BEST WITH ALL LUBES. IT'S BETTER TO USE TOO LITTLE THAN TOO MUCH!!!"

super6 wrote: "Here's the link for the replacement RWS trigger spring. This spring will make the single biggest improvement for your T05 trigger on any RWS/Diana gun. The rest is a slight amount of polishing and a very tiny amount of moly. Back to work......"

Stage 1 Results

super6 wrote: "RWS 34 results: using JSB 8.44 Exacts....10 shot string. High velocity: 1023. Low velocity: 886.2. Extreme spread: 137.7. Avg. deviation: 43.58. Average Velocity: 943.5fps (793.85 out of the box)."

"As you can see, the numbers are all over the lot but should settle down with more shooting. I believe the spread problem is the result of using a new Tesla seal which was a much tighter fit than the Apex seals I've used, and which will probably arrive tomorrow. Because it is slightly oversize it 'pushed' more of the SuperLube into the compression area and the first shot resulted in noticeable dieseling but nothing apparent after that."

"There are two ways to address the 'problem'....shoot the gun until it settles down or tear it down and sand a little off the seal and put it all back together. As I need to take it down for the Stage 2 Project, if my parts arrive tomorrow, I'll set it aside for now. If I toss out the high and low shots the average velocity with the mid-weight JSB 8.44 pellets is 940.6fps."

"Sooooo......I think I can say that the Pyramyd Air Venturi RWS spring and guide kit is a 'qualified' success IF used in conjunction with a routine tune. The firing cycle seems quicker with a slightly sharper thunk than before and no discernable twang. Cocking effort is maybe 10-15% more, if that much, and very smooth. And pellet velocity is up about 150fps with a good mid-weight quality pellet."

super6 wrote: "I've decided to finish the B28 tune tomorrow, assuming my Apex seals arrive. I want to keep my remaining Tesla seal unmodified in case I need a slightly oversized high quality seal for another gun. The original B28 seal is pretty rough so I'm tossing it and the RWS seal from the 34 is probably useable with some touch-up but I'll hang on to it for a spare. So, tomorrow I'll finish up the B28 and post the numbers, and begin the Stage 2 RWS 34 project."

"C.A.P. or Chris had to tend to some personal business today. The Uber B28/350 project is going almost too well as his B28's stock is having problems handling all the additional power. He has a straight-forward fix for that. Expect some numbers mid-week...make that kickass numbers! Late in the week I should have my 350 done with the same upgrade. We want to make sure both guns respond the same. So far the accuracy is excellent. Later. Ray"

C.A.P wrote: "Yes Ray I was hit with the slow down factor. I have shot this big one a few times but decided against further potential damage. I will pillar the stock. At the breech and the trigger. I know this along with my new stock screws have the best chance of success."

tunedairguns wrote: "good info guys. thanks"

super6 wrote: "Well my parts arrived but life, as in taxes, got in my way today. Will try to get some work done this evening and post my progress. Here's a little tease. The picture (ignore the B28 piston) shows the stock 34 spring and rear guide and below it is the (drum roll) new 34 Stage 2 spring. Ta daa! More shall be revealed......."

super6 wrote: "I'm back after spending a lovely day with the Veterans Administration in Prescott, AZ, along with about 5 hours of driving. Due to a number of requests, I'll post some pix and info on my Gamo 1250 and then I'll be working on the 34 upgrade and post my progress later this evening. My apologies to those back east."

"Even if I have the 34 back together tonight, I will hold off firing it until tomorrow since I need to find a few items to reinforce the stock. Working with Chris on the B28/350 super gun project, it is apparent that the standard stocks need some work to handle the power levels we're working with. It's an easy fix and I'm sure he'll post some pix this evening as will I tomorrow. At this point, all that remains to be done is for Chris to get some chrono numbers and post them. Should have those very soon but be patient as I'm technically 'retired' while Chris has a family to support, as in having a real job."

"So, I'll proceed with the 34 Stage 2, finish the B28 tune, and then do the super gun makeover to my RWS 350. Hopefully, some of you will be able to benefit from our experiments and/or come up with some new projects for other guns. Mine and Chris's focus is in making more powerful but civilized hunting guns. Our goal is 900+fps guns using medium to heavy pellets for humane and efficient kills. We could care less about high fps numbers with super light pellets. Plus we're having fun trying different things that we haven't heard of others trying. Ray"

Stage 2: A Magnum Spring That Wouldn't Cooperate

super6 wrote: "I'm baaack! Stage 2 of the RWS 34 is not performing up to expectations though on paper it should be a more powerful package than the Pyramyd Air Venturi RWS spring/guide which worked surprising well. I have a few more tricks to, hopefully, unlock the full potential of this 'magnum' spring. Here is a recap of the numbers, all using 8.44gr JSB Exacts and 10-shot strings."

"Stock gun out of the box: 793.9fps avg. Air Venturi Spring/Guide Upgrade: 943.5fps avg. (Stage 1). Magnum Spring Upgrade: 887.7fps avg. (Stage 2)."

"Both Stage 1&2 are very civilized shooters with easy smooth cocking and no negative tradeoffs. We'll have the final results within a few hours (back and forth with Chris)."

"UPDATE: The B-28/RWS 350 project is done. But Chris's chrono has not yet arrived so no hard numbers to post. His gut feel is very positive....stay tuned. I'll post pix later on the stock upgrades to handle the additonal power levels we've been playing with. Easy and looks professional."

C.A.P wrote: "As Ray has said the B28/350 is shooting. I have about 250 rounds through her. The seals are starting to jive. I will have a chrony this week to verify the results. Its definitely a shooter !"

super6 wrote: "After some significant changes but still using the same spring, I've come up with almost a repeat of the first go-round with Stage 2. Just fired off a 10-shot string and came up with an avg. of 880.9fps, still using the 8.44 JSB Exacts."

"Both Chris and I are scratching our heads on this one. On paper, this spring should be the cat's meow for the 34. In fact we were a little worried it might be too much spring. I'm done playing tonight. Maybe we'll come up with a different approach tomorrow. To be cont............"

C.A.P wrote: "Math doesn't always work in real time Ray. This is an example of that right in front of our faces. Its still is hard to believe that that spring has no real power to speak of."

super6 wrote: "Well, I gave up on the 'magnum' spring which looked so good on paper. It's Maccari's E5800 Heavy Spring. So, I went back to the Pyramyd Air Venturi spring/guide kit. I removed a spacer and added two polished stainless washers in the piston. Put a 10-shot string through the chrono using 8.44gr JSB Exacts with a 888.2fps avg."

"The results are actually good for a couple of reasons due to the piston seal. It is actually an Apex and it is a little oversize and fits VERY snug and it is acting like a squeegee in the combustion area. Plus the seal needs to break-in more and the spread will continue to shrink. I can either disassemble the gun and take a little off the seal, by hand, or just shoot the gun and it will self-correct. It's such a pleasant gun to shoot, I'll go that way. I know it won't be long before it's solidly in the 900's with a much smaller average deviation. Since I'm tuning for myself, I can do it this way. If I were using Gamo Hunters, I'd already be well into the 900+ range. If I had used a new RWS piston seal I would be in the 900s now with the JSBs as it is slightly smaller than the Apex."

"I had wanted an off-the-shelf spring and the E5800 looked like the way to go on paper but it turned out to be roughly equivalent to the Air Venturi kit. There are other springs which would definitely be a big improvement but I would need to shorten them and refinish the ends, which I know how to do properly, but I was trying for an easy drop-in improvement that the home tuners could easily do. In the near future I'll post an update as I fully expect the numbers to improve."

"Tomorrow I'll show how to pillar your stock to better handle recoil (a must for the B28/RWS350 upgrade) and give your gun a more professional look...it's cheap and easy. And I'll slap the B28 back together with no more than a tune, piston seal, and stainless washers and we'll see how well it responds. Chris will have his chrono this week and will post the numbers for his 'B280' super gun. If it is a success, I'll be doing my 350, as I have all I need on hand to match his B280. And I'll keep putting pellets through the 34."

tunedairguns wrote: "shoot the 34 and keep us updated ."

Robin A wrote: "This is getting good,more info.and pic's please........................Robin"

Pillaring the Stock

Bob wrote: "Hey Ray, Great write up. Please explain the (how to pillar your stock). Did you make the pillar and how or buy and where. The soft wood on the chinese AG need this mod. Thanks Bob"

C.A.P wrote: "Any good hardware store will have them. they are shoulder bushings. They work great."

Bob wrote: "Shoulder bushings, Thanks Chris"

C.A.P wrote: "If you cant find any let me know I have a few extra!"

Bob wrote: "Thanks Chris, I have about 4 store to check on. One of them should have them. McLendon is a great hardware store, has all the old stuff too. I checked their web page, didn't see any, but I'll stop by and ask."

super6 wrote: "Bob: I'll post photos of the bushings and instructions tomorrow (Fri.). If you find some they will be in the nuts and bolts section where all the nylon stuff is located. You want the black ones with a 0.260 O.D. if you can't wait on me. It's been a hectic week....sorry. Ray"

super6 wrote: "Search for the pictured nylon bushings in the nuts and bolts section of a good hardware store. It is unlikely you'll find them at a Home Depot. You want the ones that are 0.26 O.D. (the barrel not the shoulder). You may need different sizes depending on your gun. This size is correct for B28's and RWS 350's and 34's."

"Enlarge, carefully, the forearm bolt holes starting with a 0.25 drill bit. Then step up to a slightly larger bit but no more than 0.26. You want a snug fit but don't force it or damage the wood. Insert bushing in hole and push it all the way in. Inside the forearm, mark the bushing flush with the wood. Remove the bushing and cut off the excess. Reinsert the bushing, install the factory washer, and then reuse the original phillips head screw or find the same size metric allen head screw for a more professional look."

"The original washers on the B28 are not blued, so you may want to blue them or replace them, so everything matches."

"Now the recoil forces are more evenly diffused through the wood in the forearm, minimizing the chance for cracks or the holes becoming elongated. It's cheaper than bronze cups from MAC1. And it just plain looks better. Ray"

Wrapping Up

C.A.P wrote: "Well After some testing all day and many spring changes and disassembles. I have some preliminary results on the 28 or 280. I have had a barrel breech concern since I received the gun. Its a tad off center and the pellets never went in easy. I opened it up to allow them to go in easier. Its the lesser of two evils."

"I also do not like their attempt at a choke. (many of you know Im a fan of chopping them down), Well this one seen a 3 inch chop and re crown. It was a big help in accuracy and speed. I seen a 25 fps increase and my groups were better with much less recoil."

"I tried a custom spring of my own design and 3 others, I seen numbers anywhere from 929 to 575 with 14.3 grain pellets. All varying with the same or different springs. The lower # wee attributed to the breech issue I think. I had to really seat these pellets in and I would never own a gun that was that way. (Its the perfectionist in me) I re checked the piston seal for exactness and went after the breech. I started out with a stock spring that was around 837 to 840. I knew the gun was a 850 to 875 capable gun with a few tweaks. It seen varying #'s as the pellets were different and some were useless in this breech. The larger rear skirt ones worked best. I did not have a huge selection to work with, but I do think a good FTS or JSB would have helped. Now I say 'WOULD' as the barrel breech is definitely an issue as I'm so inconsistent in speeds and each shot is so different from the blow by that its hard to get an average. I have tried to shoot one and wait 5 min, then shoot another. So far with the combo I'm running now its about 895 to 925 with the 14.2 RWS super H. I know that there is a bit more once I get the new barrel and breech that lines up and does not need to be opened up so much."

"I have contacted the place I ordered the gun from and have a new barrel and breech coming. I think its key to be dead center when tuning for power in these guns. Its been a Achilles heel for me. I will report full details with actual chrony numbers as soon as I get the new barrel breech."

"Over all I think I have already accomplished a big goal. 900+fps with a .22 and a 14.3 grain pellet. I think there is a tad more and I will push it as far as possible."

"Oh yeah! For those asking about accuracy and shoot characteristics. Its very stout, real recoil with 1/4 inch groups standing shooting at 10 meters. So far all has been good. Its been a lot of experimenting and work but its fun along the way! Ill report back ASAP! C.A.P"

Robin A wrote: "Keep it coming,all this info is great.................Thanks, Robin"

super6 wrote: "Some comments: C.A.P., with me in a supporting role, was attempting to upgrade the B28 (and the 350 by default) to a true magnum shooter while I was attempting to bump up the 34 to a higher level especially for those with .22 guns. Right now, Chris has a B28 consistently shooting around 890-925fps with a very screwed up breech. All the RWS 350 numbers are in the low 800's except for one that is in the neighborhood of 870fps. So, by any standard, he's done a great job using a 350 clone that cost about $155 plus shipping for both of us. I also have to thank Rich in Mich for his feedback and support. I believe along with Chris that a new barrel/breech block should put his numbers close to 950fps with the 14.3 Crosmans. That would be an excellent result for all his efforts to-date."

"As far as my 34, I'll order some RWS piston seals and replace the over-sized and far too tight Apex seal currently in the gun. Just that should improve my numbers considerably. We've both learned a lot about springs and that the basic numbers about a certain spring are not enough to predict its performance in a certain model gun. Other factors to consider are spring rebound, the size of the compression area and the amount of air to be compressed, among others. So, it's part physics, and part dumb luck. More to come...... Ray"